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Author: Subject: Sodium Polyacrylate pyrolysis to Acrylates?
Catslovechemistytoo
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[*] posted on 2-1-2025 at 20:59
Sodium Polyacrylate pyrolysis to Acrylates?


Is it possible to somehow synthesize acrylic acid or it's esters from sodium polyacrylate? How about pyrolizing sodium polyacrylate to distill the monomeric form? Or maybe hydrolize it in acidic methanol/ethanol before distilling.

There just seems to be no easy way for getting acrylic acid esters in monomer form unlike methacrylate esters.
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chempyre235
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[*] posted on 3-1-2025 at 06:20


I would only be guessing on procedures for pyrolysis, but I do know that many organic acids decarboxylate on heating in salt form. Acetone is made from calcium acetate this way, I believe. (Please correct me if I'm wrong.) Benzene is also produced from sodium benzoate in the lab using this method.

If you are just needing the acid, and aren't specifically aiming to develop a process, acrylic acid and methacrylic acid are both available from this site. They'll run about $30 for 400g. They also carry salts of this acid, and the anhydride for making acrylate esters and amides. They also have quite a few different acrylate esters.

[Edited on 1/3/2025 by chempyre235]
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Boffis
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[*] posted on 4-1-2025 at 07:12


How does the sodium salt respond to dilute mineral acid? Does it still swell up like the sodium salt in water? I am wondering if you would be better off pyrolysing the free acid.

Alternatively, could you esterify the salt by treating it with absolute ethanol and HCl gas.
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[*] posted on 7-1-2025 at 16:19


Quote: Originally posted by Boffis  

Alternatively, could you esterify the salt by treating it with absolute ethanol and HCl gas.


With dilute acids it swells, yes. Like with water.
That's what I was thinking as well. Refluxing in with MeOH+HCl or H2SO4 for few hours, neutralize the acid and pyrolize it. Will this work? The ester should be better at pyrolysis than the free acid as far as I understand.
I have read that acrylates get destroyed during pyrolysis with almost no monomer collected in the receiving flask, unlike methacrylates which undergo depolymerisation perfectly fine.
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bnull
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[*] posted on 8-1-2025 at 06:05


Try refluxing the free acid with a high boiling solvent instead of pyrolysis. According to patent US4293347, it happens above 275 °C, with an alkyl phthalate as solvent.

It seems everyone is more interested in the decomposition of polyacrylate; pretty much everything I found was related to degradation of the polymer or decarboxylation by Fenton or ultrasound.




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[*] posted on 8-1-2025 at 11:49


Quote: Originally posted by bnull  
Try refluxing the free acid with a high boiling solvent instead of pyrolysis. According to patent US4293347, it happens above 275 °C, with an alkyl phthalate as solvent.


Interesting thank you. Which solvent can be used instead of dialkylphtalate? How about using paraffin oil? Although, paraffin oil boils and smokes at lower temperatures, maybe it can be distilled to discard lower boiling compounds?

And how to extract the acrylic acid if the reaction was successful? Vacuum distillation? Or azeotropically distill it with water (although I'm not sure if Acrylic acid forms azeotrope with water).
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[*] posted on 9-1-2025 at 15:04


I don't know. Lower boiling solvents, if they work at all, may require longer reflux times to work. The few solvents I found close enough to phthalates were hydrogenated cottonseed oil, which boils at about 260 °C, and refined avocado oil, which starts smoking at 270 °C. Give paraffin oil a try. If it works, good; if it doesn't, there are the other two oils. I don't want to make you buy useless stuff, though.

I wonder if you can use water to extract acrylic acid from the first solvent. If so, you can use water first, then extract the acid from water with n-heptane, and finally vacuum distill n-heptane out. Acrylic acid is miscible and forms an azeotrope with water, and is very soluble in n-heptane.

You may want to read this, even if only for the references: Acrylic Acid Production: Separation and Purification. There's also this thesis about "Thermal stability and degradation of some polyacrylate salts", by Angus Alston.

Edit: Missing words.

[Edited on 10-1-2025 by bnull]




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[*] posted on 13-1-2025 at 13:44


Quote: Originally posted by bnull  
I don't know. Lower boiling solvents, if they work at all, may require longer reflux times to work. The few solvents I found close enough to phthalates were hydrogenated cottonseed oil, which boils at about 260 °C, and refined avocado oil, which starts smoking at 270 °C. Give paraffin oil a try. If it works, good; if it doesn't, there are the other two oils. I don't want to make you buy useless stuff, though.

I wonder if you can use water to extract acrylic acid from the first solvent. If so, you can use water first, then extract the acid from water with n-heptane, and finally vacuum distill n-heptane out. Acrylic acid is miscible and forms an azeotrope with water, and is very soluble in n-heptane.

[Edited on 10-1-2025 by bnull]


Maybe it can be extracted with methanol? Methanol doesn't mix with paraffin oil, not sure about hydrogenated plant oils though. The convenience is that the methyl ester can be made straight away if extracting with methanol. I'm still doubtful that it will work.
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